In an attempt to improve the performance under frequency selective fading environment, we develop in this paper an orthogonal frequency division multiplex (OFDM) system in which adaptive interleaving is applied. The adaptive interleaving is a method that assigns symbols adaptively to the subcarriers in order to cope with frequency selective fading based on a channel state information (CSI) sent back from the reception end. The concept of adaptive interleaving is to maximize a free Euclidean distance in the limited interleave size. In this paper, we extend the method by an introduction of bit interleaving and multiple trellis coded modulation (MTCM). MTCM assigns two or more symbols to one trellis branch and shows good performance in frequency selective fading. If we could assign those set of symbols with an aid of the adaptive interleaving, the performance improvement can be expected. Another improvement method considered in this paper is the use of bit interleaving. The bit interleaving techniques randomize the effect of channel more efficiently compared to the case of symbols interleaving. Thus the further performance improvement is expected. One draw back is that since the interleaving process is done in bit level, bit interleaving can not be applied to TCM nor MTCM. In this paper, we mainly focus on adaptive bit and symbol interleaving and discuss the performance from the point of interleaving effect, and the error correcting code (convolutional code and MTCM).

In recent years, sliding electric contacts came to be often used under very severe conditions such as high temperature, extremely low temperature, high vacuum, etc. Conventionally, solid lubricants having excellent properties in lubricating performance are generally used compositely with a metal of high electric conductivity, because of their high electrical resistivity. In the present study, we proved that more excellent sliding electrical contacts can be produced with a design made by controlling the distribution on contact surface of a solid lubricant having excellent lubricating performance and of a metal with high electric conductivity through expansion of Greenwood's theory.

Many congestion control mechanisms have been proposed to solve the problems of a high loss rate and inefficient utilization of network resources in the present Internet. This problem is caused by competition between traffic flows while the network is congested. Differentiated Services (DiffServ) architecture permits the allocation of various levels of traffic resource requirements needed for Quality of Service (QoS). Random Early Detection (RED) is an efficient mechanism to pre-drop packets before actual congestion occurs, and it is capable of introducing a random early packet dropping scheme, and based on the queue length in reaching a certain degree of fairness for resource utilization. However, it still suffers from a lack of robustness among light traffic load, or in heavy traffic load using fixed RED parameters. In this paper, we modified the RED scheme and proposed a novel adaptive RED model, which we named the OURED model, to enhance the robustness of resource utilization so that it could be utilized in the DiffServ edge router. The OURED model introduces two additional packet dropping traces, one is Over Random Early Detection (ORED), which is used to speed up the dropping of packets when the actual rate is higher than the target rate, and the other one is the Under Random Early Detection (URED), used to slow down the packet dropping rate in the reverse situation. The simulation results show that OURED is not only more robust than MRED in resource utilization, but that it also can be implement efficiently in the DiffServ edge router.

TLSP (Thread-Level Speculative Parallel processing) architecture is a growing processor architecture. Parallelism of a program executed on this architecture is ruled by the combination of techniques which relax data dependences. In this paper, we evaluate the limits of parallelism of the TLSP architecture by using abstract machine models. We have three major results. First, if we use solely each technique which relaxes data dependences, "renaming" has a large effect on the TLSP architecture. Second, combinatorial use of "memory disambiguation" and "renaming" leads to huge parallelism. Third, constant effects are obtained by concurrent use of "value prediction" and other techniques.

Electron field emission from polycrystalline diamond films has been investigated. Electron emission was measured locally at randomly chosen point on a diamond film fabricated by a microwave plasma chemical deposition method. In the original film, there were some points with a large emission current where flaws were found after the measurements, some points with a small and stable emission current without any flaw, and the other points with no emission. At the point of no emission, the film was electrically broken down by applying a high voltage. After the intentional breaking down, a small and stable emission always appeared there with no flaw. The maximum emission current extracted from an emission site was usually 1µA with no structural flaw found after the measurements. By using a simple model of emission site consisting of a core conductor embedded in insulator, the limitation of emission current is estimated from heating by the current and heat transfer to the insulator.

Our work introduces a speech enhancement algorithm that modifies on-line the spectral representation of degraded speech to approximate the spectral coefficients of high quality speech. The proposed framework is based on the application of Discrete Fourier Transform (DFT) to a large ensemble of clean speech frames and the estimation of parametric, heavy-tail non-Gaussian probability distributions for the spectral magnitude. Each clean spectral band possesses a unique pdf. This is selected according to the smallest Kullback-Leibler divergence between each candidate heavy-tail pdf and the non-parametric pdf of the magnitude of each spectral band of the clean ensemble. The parameters of the distributions are derived by Maximum Likelihood Estimation (MLE). A maximum a-posteriori (MAP) formulation of the degraded spectral bands leads to soft threshold functions, optimally derived from the statistics of each spectral band and effectively reducing white and slowly varying coloured Gaussian noise. We evaluate the new algorithm on the task of improving the quality of speech perception as well as Automatic Speech Recognition (ASR) and demonstrate its robustness at SNRs as low as 0 dB.

Content addressable memory (CAM) is one of the functional memories which realize word-parallel equivalence search. Since a CAM unit is generally used in a particular application program, we consider that appropriate design for CAM units is required depending on the requirements for the application program. This paper proposes a hardware/software cosynthesis system for CAM processors. The input of the system is an application program written in C including CAM functions and a constraint for execution time (or CAM processor area). Its output is hardware descriptions of a synthesized processor and a binary code executed on it. Based on the branch-and-bound method, the system determines which CAM function is realized by a hardware and which CAM function is realized by a software with meeting the given timing constraint (or area constraint) and minimizing the CAM processor area (or execution time of the application program). We expect that we can realize optimal CAM processor design for an application program. Experimental results for several application programs show that we can obtain a CAM processor whose area is minimum with meeting the given timing constraint.

We show that a randomized addition-sub-traction chains countermeasure against side channel attacks is vulnerable to an SPA attack, which is a kind of side channel attack, under distinguishability between addition and doubling. The side channel attack takes advantage of information leaked during execution of a cryptographic procedure. The randomized addition-subtraction chains countermeasure was proposed by Oswald-Aigner, and is based on a random decision inserted into computations. However, the question of its immunity to side channel attacks is still controversial. The randomized addition-subtraction chains countermeasure has security flaw in timing attacks, another kind of side channel attack. We have implemented the proposed attack algorithm, whose input is a set of AD sequences, which consist of the characters "A" and "D" to indicate addition and doubling, respectively. Our program has clarified the effectiveness of the attack. The attack algorithm could actually detect secret scalars for given AD sequences. The average time to detect a 160-bit scalar was about 6 milliseconds, and only 30 AD sequences were enough to detect such a scalar. Compared with other countermeasures against side channel attacks, the randomized addition-subtraction chains countermeasure is much slower.

Optical Burst Switching (OBS) is one of the most important switching technologies in future optical Internet. One of critical design issues in OBS is how to reduce burst dropping resulting from resource contention. Especially when traffic load is high, there should be frequent deflection routing as well as more contentions in an optical burst-switched network. The burst loss performance can be improved by implementing a proper deflection routing scheme. In this paper, we propose a limited deflection routing scheme to prevent injudicious deflection routing. The proposed scheme reduces unnecessary contentions resulting from deflection routing itself, increasing the utilization of network resource such as channels. Simulation tests were performed to evaluate the performance of the proposed scheme.

We discuss applications of quantum computation to geometric data processing. Especially, we give efficient algorithms for intersection problems and proximity problems. Our algorithms are based on Brassard et al. 's amplitude amplification method, and analogous to Buhrman et al. 's algorithm for element distinctness. Revealing these applications is useful for classifying geometric problems, and also emphasizing potential usefulness of quantum computation in geometric data processing. Thus, the results will promote research and development of quantum computers and algorithms.

In a bidirectional wavelength-reused system, polarization control is used to reduce power penalty induced by coherent mixing of the signal with Rayleigh backscattering. The reduction of the effect of Rayleigh backscattering is theoretical study and experimental demonstration. For a 50km, 10Gb/s bidirectional transmission system, an error floor of about 510-10 under the worst polarization state is occurred. Nevertheless, the power penalty is reduced from 3.5dB to only 0.3dB when the signals are under optimum polarization control. The results indicate that the proposed technique may find vast applications in bidirectional ring networks with add/drop as well as cross-connect nodes using wavelength-reused technology.

In this paper, we propose a new transmitter diversity. We propose a combined system with path diversity gain of the distributed antennas and frequency diversity gain of the multi-carrier. The proposed system transmits different data using several sub-carriers which are correlated, while, transmitting the same data using several sub-carriers which are decorrelated. It can achieve combined path and frequency diversity in a variable frequency selective fading channel. It provides high data rate services by transmitting the different data using each correlated carrier, and supports good quality by transmitting the same data on decorrelated carriers using multiple antennas. The proposed system is applicable to multimedia service and can achieve high quality according to channel condition. Thus, the proposed system is sufficiently flexible enough to very support a variety of video, image, voice and data services at a high level of quality.

In this paper, the Viterbi decoder containing new branch metrics of the squared Euclidean distance with multiple order phase differences is introduced in order to improve the bit error rate (BER) in the differential detection of the trellis-coded MDPSK-OFDM. The proposed Viterbi decoder is conceptually same as the sliding multiple phase differential detection method that uses the branch metric with multiple phase differences. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency. Also, the proposed algorithm can be used in the single carrier modulation.

One of the difficulties in routing problem is in wirability which is to guarantee a physical connection of a given topological route. Wirability often fails since the width of a wire is relatively large compared with the size of modules. As a possible solution, this paper proposes an incremental wiring algorithm which generates wires net-by-net without overlapping other pre-placed circuit elements. The idea is to divide a wire into a series of rectangles and handles them as modules with additional constraints to keep the shape of the wire. The algorithm was implemented and experimented on a small instance to show its promising performance.

In 1991 Girault proposed a key agreement protocol based on his new idea of self-certified public key. Later Rueppel and Oorschot showed variants of the Girault scheme. All of these key agreement protocols inherit positive features of self-certified public key so that they can provide higher security and smaller communication overhead than key agreement protocols not based on self-certified public key. Even with such novel features, rigorous security of these protocols has not been made clear yet. In this paper, we give rigorous security analysis of the original and variants of Girault key agreement protocol under several kinds of active attacker models. In particular we show that protocols are either insecure or proven as secure as the Diffie-Hellman problem over Zn with respect to the reduction among functions of computing them. Analyzed protocols include a new variant of 1-pass protocol. As opposed to the original 1-pass protocol, the new variant provides mutual implicit key authentication without increasing the number of passes.

We demonstrate a mode-locked fiber laser (MLFL) method for measuring the chromatic dispersion of long transmission fiber. In this method, device under test (DUT) is inserted in the laser cavity, and the chromatic dispersion is measured by the shift of mode-locking frequency when the lasing wavelength is changed. The experimental results of the MLFL method for a 5km-long single-mode fiber had good agreement with the conventional phase-shift method.

A novel signal processing technique using adaptive neural network algorithm is applied for the on-line detection of harmonic current components generated by nonlinear current loads in the single-phase diode bridge rectifier and it can efficiently determine the harmonic current components in real time. The validity of this active filtering processing system to compensate current harmonics is proved on the basis of simulation results.

This paper studies the necessity of local CFAR processing in CFAR detection with multisensors. This necessity is shown by comparison between centralized CFAR detection and the distributed CFAR detection scheme based on local CFAR processing, under three typical backgrounds and in several cases of mismatching ρ, the relative ratio of local clutter power level in sensors in a homogeneous background. Results show that centralized CFAR processing can not be considered as CFAR without exact prior knowledge of ρ. In addition, even if the knowledge of ρ is available, the great difference among local clutter power levels can also result in severe performance degradation of centralized CFAR processing. In contrast, the distributed CFAR detection based on local CFAR processing is not affected by ρ at all, a fact which was proposed in a previous published paper. Therefore, the CFAR processing must be made locally in sensors for CFAR detection with multisensors.

Let α and β be polygons with the same area. A Dudeney dissection of α to β is a partition of α into parts which can be reassembled to produce β in the following way. Hinge the parts of α like a chain along the perimeter of α, then fix one of the parts and without turning the pieces over, rotate the remaining parts about the fixed part to form β in such a way that the entire perimeter of α is in the interior of β and the perimeter of β consists of the dissection lines formerly in the interior of α . In this paper we discuss a special type of Dudeney dissection of convex polygons in which α is congruent to β and call it a congruent Dudeney dissection. In particular, we consider the case where all hinge points are interior to the sides of the polygon α. A convex polygon which has a congruent Dudeney dissection is called a chameleon. We determine all convex polygons which are chameleons.

A dual greedy polyhedron is defined by a system of linear inequalities, where the right-hand sides are given by a submodular function and the coefficients matrix is given by the incidence vectors of antichains of a rooted forest. Faigle and Kern introduced this concept and showed that a dual greedy algorithm works for the linear program over dual greedy polyhedra. In this paper, we show that a dual greedy polyhedron is the isomorphic image of an ordinary submodular polyhedron under the Mobius function of the underlying rooted forest. This observation enables us to reduce linear optimization problems over dual greedy polyhedra to those over ordinary submodular polyhedra. We show a new max-min theorem for intersection of two dual greedy polyhedra as well.